Embodiments of the invention relate generally to electric vehicle charging and, more particularly, to a system and method for inductive charging of an electric vehicle that provides high efficiency inductive charging. The inductive charging of the vehicle is achieved via a system that is minimally intrusive—both aesthetically and from an infrastructure perspective—to a surrounding environment, and is provided via an autonomous interaction between the electric vehicle and a charging station that provides self-alignment and mating between the electric vehicle and the charging station.
Electric vehicles (EVs) provide a zero-emissions solution for transportation in cities and, in the future, are expected to gradually replace the internal combustion engine vehicle as the primary mode of transportation. Electric vehicles are configured to use electrical energy from an external source to recharge the traction battery thereof, and thus include circuitry and connections to facilitate the recharging of the traction battery from the utility grid or another external source, for example. Typically, these circuitry and connections include a plug-in by which the electric vehicle is connected to the utility grid to receive such charging power.
Unfortunately, it is recognized that a large percentage of electric vehicle owners do not have the ability to charge at home, due to lack of an electrical outlet or space for a charger—with electric vehicle owners who live in an apartment or condominium complex being primary examples. That is, traditional corded plug-in or “hot contact” chargers may often not be available at parking lots and parking garages of an apartment or condominium complex due to concerns of the apartment/condominium owner regarding aesthetic issues (e.g., presenting a “gas station”-like appearance due to multiple charging pedestals), safety/security issues (e.g., exposed cords being vandalized or stolen for the scrap value of copper inside the cords), and/or longevity and upkeep issues (e.g., degradation of electrical contacts due to exposure to the environment, resulting in maintenance/replacement costs and a potential spark hazard to adjacent gasoline fueled vehicles). Further, corded chargers must be handled by a person at the beginning and end of each day (unplugged and plugged) to keep the battery at a good state of charge on the electric vehicle, which may be time consuming, inconvenient, and potentially forgotten by a user, thereby resulting in a car that is out of charge in the morning.
As an alternative to corded plug-in chargers, inductive charging has been used to recharge electric vehicles. Early inductive charging systems for electric vehicles used inductive paddles to solve potential safety and degradation issues typically associated with plug-in chargers. However, these inductive paddles did not address cord issues or charging convenience issues and also resulted in lower charging efficiency as compared to plug-in chargers (e.g., about 85%). More recently, modern inductive electric vehicle chargers have been designed that provide low-clutter, ground-mount charging that is an aesthetic improvement over corded charging stations and impervious to chemicals and electrically safe, as there are no exposed galvanic connections to create a shock or spark hazard. The modern inductive charging systems are also hands-free, but the spacing of the inductive transfer coils, to accommodate suspension travel and misalignment on other axes, results in reduced electrical transfer efficiencies (i.e., charging efficiencies) wherein twice as much energy is lost during the transfer as compared to the best hot contact chargers. Thus, state-of-the-art inductive charging efficiency may be in the low nineties, which is less than the 94-97% charging efficiency that is desirable and that is achievable via corded plug-in chargers (e.g., 93% vs 96.5%).
Another recent way to obtain hands free autonomy with high transfer efficiency is use of a robot function in the charger to align a hot contact connection with the charge port on a stationary vehicle. This does not solve the environmental robustness issues with hot contacts, and adds cost, reliability concerns and possibly more clutter to the already crowded urban environment.
Therefore, it is desirable to provide a hands-free, ground-level inductive charger that would be well suited to uncontrolled parking environments (like apartment parking lots and public garages) for overnight charging and is durable enough to withstand environmental factors. It is further desirable for the charging of the electric vehicle to make use of the precision of autonomous vehicle parking and modern circuit topologies, such that the ground-level inductive chargers may be as efficient as corded plug-in chargers in charging the electric vehicle.